Semiconductor device and manufacturing method thereof

ABSTRACT

In a method of manufacturing a semiconductor device, a fin structure, in which first semiconductor layers and second semiconductor layers are alternately stacked, is formed over a bottom fin structure. A sacrificial gate structure having sidewall spacers is formed over the fin structure. A source/drain region of the fin structure, which is not covered by the sacrificial gate structure, is removed. The second semiconductor layers are laterally recessed. Dielectric inner spacers are formed on lateral ends of the recessed second semiconductor layers. The first semiconductor layers are laterally recessed. A source/drain epitaxial layer is formed to contact lateral ends of the recessed first semiconductor layer. The second semiconductor layers are removed thereby releasing the first semiconductor layers in a channel region. A gate structure is formed around the first semiconductor layers.

RELATED APPLICATION

This application claims priority of U.S. Provisional Patent ApplicationNo. 62/712,868 filed on Jul. 31, 2018, the entire contents of which areincorporated herein by reference.

BACKGROUND

As the semiconductor industry has progressed into nanometer technologyprocess nodes in pursuit of higher device density, higher performance,and lower costs, challenges from both fabrication and design issues haveresulted in the development of three-dimensional designs, such as amulti-gate field effect transistor (FET), including a fin FET (Fin FET)and a gate-all-around (GAA) FET. In a Fin FET, a gate electrode isadjacent to three side surfaces of a channel region with a gatedielectric layer interposed therebetween. Because the gate structuresurrounds (wraps) the fin on three surfaces, the transistor essentiallyhas three gates controlling the current through the fin or channelregion. Unfortunately, the fourth side, the bottom part of the channelis far away from the gate electrode and thus is not under close gatecontrol. In contrast, in a GAA FET, all side surfaces of the channelregion are surrounded by the gate electrode, which allows for fullerdepletion in the channel region and results in less short-channeleffects due to steeper sub-threshold current swing (SS) and smallerdrain induced barrier lowering (DIBL). As transistor dimensions arecontinually scaled down to sub 10-15 nm technology nodes, furtherimprovements of the GAA FET are required.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIGS. 1A, 1B, 1C and 1D show various views of a GAA FET device accordingto an embodiment of the present disclosure.

FIGS. 2A, 2B, 2C and 2D show various views of a GAA FET device accordingto another embodiment of the present disclosure.

FIG. 3 shows a view of one of the various stages of a sequentialmanufacturing process for a GAA FET device according to an embodiment ofthe present disclosure.

FIG. 4 shows a view of one of the various stages of a sequentialmanufacturing process for a GAA FET device according to an embodiment ofthe present disclosure.

FIG. 5 shows a view of one of the various stages of a sequentialmanufacturing process for a GAA FET device according to an embodiment ofthe present disclosure.

FIG. 6 shows a view of one of the various stages of a sequentialmanufacturing process for a GAA FET device according to an embodiment ofthe present disclosure.

FIG. 7 shows a view of one of the various stages of a sequentialmanufacturing process for a GAA FET device according to an embodiment ofthe present disclosure.

FIG. 8 shows a view of one of the various stages of a sequentialmanufacturing process for a GAA FET device according to an embodiment ofthe present disclosure.

FIG. 9 shows a view of one of the various stages of a sequentialmanufacturing process for a GAA FET device according to an embodiment ofthe present disclosure.

FIG. 10 shows a view of one of the various stages of a sequentialmanufacturing process for a GAA FET device according to an embodiment ofthe present disclosure.

FIGS. 11A and 11B show views of one of the various stages of asequential manufacturing process for a GAA FET device according to anembodiment of the present disclosure.

FIGS. 12A and 12B show views of one of the various stages of asequential manufacturing process for a GAA FET device according to anembodiment of the present disclosure.

FIGS. 13A and 13B show views of one of the various stages of asequential manufacturing process for a GAA FET device according to anembodiment of the present disclosure.

FIGS. 14A and 14B show views of one of the various stages of asequential manufacturing process for a GAA FET device according to anembodiment of the present disclosure.

FIGS. 15A and 15B show views of one of the various stages of asequential manufacturing process for a GAA FET device according to anembodiment of the present disclosure.

FIGS. 16A and 16B show views of one of the various stages of asequential manufacturing process for a GAA FET device according to anembodiment of the present disclosure.

FIGS. 17A and 17B show views of one of the various stages of asequential manufacturing process for a GAA FET device according to anembodiment of the present disclosure.

FIGS. 18A and 18B show views of one of the various stages of asequential manufacturing process for a GAA FET device according to anembodiment of the present disclosure.

FIGS. 19A and 19B show views of one of the various stages of asequential manufacturing process for a GAA FET device according to anembodiment of the present disclosure.

FIGS. 20A and 20B show views of one of the various stages of asequential manufacturing process for a GAA FET device according to anembodiment of the present disclosure.

FIGS. 21A and 21B show views of one of the various stages of asequential manufacturing process for a GAA FET device according to anembodiment of the present disclosure.

FIGS. 22A and 22B show views of one of the various stages of asequential manufacturing process for a GAA FET device according toanother embodiment of the present disclosure.

FIGS. 23A and 23B show views of one of the various stages of asequential manufacturing process for a GAA FET device according toanother embodiment of the present disclosure.

FIGS. 24A and 24B show views of one of the various stages of asequential manufacturing process for a GAA FET device according toanother embodiment of the present disclosure.

FIGS. 25A and 25B show views of one of the various stages of asequential manufacturing process for a GAA FET device according toanother embodiment of the present disclosure.

FIGS. 26A and 26B show views of one of the various stages of asequential manufacturing process for a GAA FET device according toanother embodiment of the present disclosure.

FIGS. 27A and 27B show views of one of the various stages of asequential manufacturing process for a GAA FET device according toanother embodiment of the present disclosure.

FIGS. 28A and 28B show views of one of the various stages of asequential manufacturing process for a GAA FET device according toanother embodiment of the present disclosure.

FIGS. 29A and 29B show views of one of the various stages of asequential manufacturing process for a GAA FET device according toanother embodiment of the present disclosure.

FIGS. 30A and 30B show views of one of the various stages of asequential manufacturing process for a GAA FET device according toanother embodiment of the present disclosure.

FIGS. 31A and 31B show views of one of the various stages of asequential manufacturing process for a GAA FET device according toanother embodiment of the present disclosure.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof the invention. Specific embodiments or examples of components andarrangements are described below to simplify the present disclosure.These are, of course, merely examples and are not intended to belimiting. For example, dimensions of elements are not limited to thedisclosed range or values, but may depend upon process conditions and/ordesired properties of the device. Moreover, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed interposing the first and second features, suchthat the first and second features may not be in direct contact. Variousfeatures may be arbitrarily drawn in different scales for simplicity andclarity.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly. In addition, the term“made of” may mean either “comprising” or “consisting of.” In thepresent disclosure, a phrase “one of A, B and C” means “A, B and/or C”(A, B, C, A and B, A and C, B and C, or A, B and C), and does not meanone element from A, one element from B and one element from C, unlessotherwise described.

In the following embodiments, material, configurations, dimensions,operations and/or processes of one embodiment may be employed in anotherembodiment, unless otherwise described, and detailed explanation thereofmay be omitted.

High mobility channel materials and device architectures have beenstudied to extend the life of Moore's law in recent 10 years. Pure Geand SiGe having a high Ge concentration are promising candidates forsuch materials due to their material property of higher intrinsic holeand electron mobility. For well-tempered device scaling of Lg<12 nm,nanowire or nanosheet structures will be employed to provide bettershort channel controlling. Therefore, Ge or SiGe nanowire devices areconsidered as promising and potential candidates for further scaled-downlogic device application. For superior Ge nanowire device performance,there are several issues to be solved, for example, (1) high interfacialstate density (Dit) under gate sidewall spacers and (2) high deviceleakage current due to narrow band-gap of Ge (0.66 eV), relative to Si(1.2 eV).

In the present disclosure, a device structure and a method ofmanufacturing thereof to solve the issues as set forth above arepresented.

FIG. 1A-1D show various views of a GAA FET device according to anembodiment of the present disclosure. FIG. 1A shows a cross sectionalview along the X direction, in which a fin structure and channels(nanowires) extend. FIGS. 1B, 1C and 1D show cross sectional views alongthe Y direction, in which a gate electrode extends. FIG. 1B is the crosssectional view corresponding to line A-A′ of FIG. 1A cutting the centerof channels. FIG. 1C is the cross sectional view corresponding to lineB-B′ of FIG. 1A cutting the center of a gate sidewall spacer. FIG. 1D isthe cross sectional view corresponding to line C-C′ of FIG. 1A cutting asource/drain epitaxial layer. In some embodiments, the GAA FET isn-channel FET.

As shown in FIGS. 1A-1D, a bottom fin structure 11 is disposed over asubstrate 10. A plurality of semiconductor wires 20, as channels, arevertically arranged over the bottom fin structure 11. Although fivesemiconductor wires 20 are shown in FIGS. 1A and 1B, the number ofvertically arranged semiconductor wires 20 is not limited to five, andit can be as small as one and up to 15-20. In some embodiments, thesemiconductor wires 20 are made of Si_(1-x)Ge_(x), where x is equal toor more than about 0.5, or Ge (x=1.0). In some embodiments, one or morefin liner layers 35 are disposed on side faces of the bottom finstructure 11. In certain embodiments, the fin liner layers 35 include afirst fin liner layer 35A disposed in contact with the bottom finstructure 11 and a second fin liner layer 35B made of a differentmaterial than the first fin liner layer 35A and disposed over the firstfin liner layer 35A. In some embodiments, at least the uppermost portionof the bottom fin structure 11 includes a layer made of SiGe.

A gate structure 100 includes a gate dielectric layer 104 wrappingaround the semiconductor wires 20 and a gate electrode layer 108disposed over the gate dielectric layer 104. In some embodiments, aninterfacial layer 102 is disposed between the gate dielectric layer 104and the semiconductor wires 20. In some embodiments, one or more workfunction adjustment layers 106 are disposed between the gate electrodelayer 108 and the gate dielectric layer 104. In some embodiments, thegate electrode layer 108 is not disposed between the semiconductornanowires 20 and the work function adjustment layer 106 fill gapsbetween adjacent semiconductor wires 20. In other embodiments, the gateelectrode layer 108 wraps around the semiconductor wires, as well as theinterfacial layer 102, the gate dielectric layer 104 and the workfunction adjustment layer 106. Further, as shown in FIGS. 1A and 1C,gate sidewall spacers 55 are disposed opposing side faces of the gatestructure 100.

Further, a source/drain epitaxial layer 80 is disposed to be connectedto horizontal ends of the semiconductor wires 20. As shown in FIG. 1A,the horizontal ends of the semiconductor wires 20 have a concave V-shapeor U-Shape, A liner layer 85, which may be a contact etch stop layer(CESL), is disposed over the source/drain epitaxial layer 80, and aninterlayer dielectric (ILD) layer 90 is disposed over the liner layer85. In some embodiments, the source/drain epitaxial layer 80 is made ofa semiconductor material having a higher energy band gap than thesemiconductor material of the semiconductor wires 20. In certainembodiments, the source/drain epitaxial layer 80 is made of Si dopedwith P (SiP).

The GAA FET shown in FIGS. 1A-1D further includes dielectric innerspacers 62 disposed between the gate structure 100 disposed betweenadjacent semiconductor wires 20 and the source/drain epitaxial layer 80.Further, a dielectric layer 60 made of the same material as thedielectric inner spacers 62 is disposed between the source/drainepitaxial layer 80 and the bottom fin structure 11.

In some embodiments, as shown in FIG. 1A, the interface between at leastone of the semiconductor wires 20 and the source/drain epitaxial layer80 is located under one of the gate sidewall spacers 55. In certainembodiments, the location under one of the gate sidewall spacers 55corresponds to a cross section (Y-Z plane) cutting the center of thegate sidewall spacer 55 in the X direction. In some embodiments, theinterface is located closer to the gate structure 100 than the centerline (line B-B′ of FIG. 1A) of the gate sidewall spacer 55. In someembodiments, an entirety of the dielectric inner spacers 62 is locatedunder the gate sidewall spacers 55.

In some embodiments, the gate sidewall spacers 55 are not in contactwith the semiconductor wires 20.

FIG. 2A-2D show various views of a GAA FET device according to anotherembodiment of the present disclosure. FIG. 2A shows a cross sectionalview along the X direction, in which a fin structure and channels(nanowires) extend. FIGS. 2B, 2C and 2D shows cross sectional viewsalong the Y direction, in which a gate electrode extend. FIG. 2B is thecross sectional view corresponding to line A-A′ of FIG. 2A cutting thecenter of channels. FIG. 2C is the cross sectional view corresponding toline B-B′ of FIG. 2A cutting the center of a first gate sidewall spacer.FIG. 2D is the cross sectional view corresponding to line C-C′ of FIG.2A cutting a source/drain epitaxial layer. In some embodiments, the GAAFET is n-channel FET.

As shown in FIGS. 2A-2D, a bottom fin structure 11 is disposed over asubstrate 10. A plurality of semiconductor wires 20, as channels, arevertically arranged over the bottom fin structure 11. Although fivesemiconductor wires 20 are shown in FIGS. 2A and 2B, the number ofvertically arranged semiconductor wires 20 is not limited to five, andit can be as small as one and up to 15-20. In some embodiments, thesemiconductor wires 20 are made of Si_(1-x)Ge_(x), where x is equal toor more than about 0.5, or Ge (x=1.0). In some embodiments, one or morefin liner layers 35 are disposed on side faces of the bottom finstructure 11. In certain embodiments, the fin liner layers 35 include afirst fin liner layer 35A disposed in contact with the bottom finstructure 11 and a second fin liner layer 35B made of a differentmaterial than the first fin liner layer 35A and disposed over the firstfin liner layer 35A. In some embodiments, at least the uppermost portionof the bottom fin structure 11 includes a layer made of SiGe.

A gate structure 100 includes a gate dielectric layer 104 wrappingaround the semiconductor wires 20 and a gate electrode layer 108disposed over the gate dielectric layer 104. In some embodiments, aninterfacial layer 102 is disposed between the gate dielectric layer 104and the semiconductor wires 20. In some embodiments, one or more workfunction adjustment layers 106 are disposed between the gate electrodelayer 108 and the gate dielectric layer 104. In some embodiments, thegate electrode layer 108 is not disposed between the semiconductornanowires 20 and the work function adjustment layer 106 fill gapsbetween adjacent semiconductor wires 20. In other embodiments, the gateelectrode layer 108 wraps around the semiconductor wires, as well as theinterfacial layer 102, the gate dielectric layer 104 and the workfunction adjustment layer 106. Further, as shown in FIGS. 2A and 2C,first gate sidewall spacers 55 are disposed opposing side faces of thegate structure 100.

Further, a source/drain epitaxial layer 80 is disposed to be connectedto horizontal ends of the semiconductor wires 20. As shown in FIG. 2A,the horizontal ends of the semiconductor wires 20 has a concave V-shapeor U-Shape. A liner layer 85, which may be a contact etch stop layer(CESL), is disposed over the source/drain epitaxial layer 80, and aninterlayer dielectric (ILD) layer 90 is disposed over the liner layer85. In some embodiments, the source/drain epitaxial layer 80 is made ofa semiconductor material having a higher energy band gap than thesemiconductor material of the semiconductor wires 20. In certainembodiments, the source/drain epitaxial layer 80 is made of Si dopedwith P (SiP).

The GAA FET shown in FIGS. 2A-2D further includes dielectric innerspacers 62 disposed between the gate structure 100 disposed betweenadjacent semiconductor wires 20 and the source/drain epitaxial layer 80.Further, a dielectric layer 60 made of the same material as thedielectric inner spacers 62 is disposed between the source/drainepitaxial layer 80 and the bottom fin structure 11. In addition, secondside wall spacers 64 made of the same material as the dielectric innerspacers 62 are disposed between the first gate sidewall spacers 55 andthe liner layer 85 as shown in FIG. 2A.

In some embodiments, as shown in FIG. 2A, the interface between at leastone of the semiconductor wires 20 and the source/drain epitaxial layer80 is located under one of the first gate sidewall spacers 55. Incertain embodiments, the location under one of the first gate sidewallspacers 55 corresponds to a cross section (Y-Z plane) cutting the centerof the first gate sidewall spacer 55 in the X direction. In someembodiments, the interface is located closer to the gate structure 100than the center line (line B-B′ of FIG. 2A) of the first gate sidewallspacer 55. In some embodiments, an entirety of the dielectric innerspacers 62 is located under the first gate sidewall spacers 55. In otherembodiments, the interface between at least one of the dielectric innerspacers 62 and the source/drain epitaxial layers 80 is located outside aregion under one of the first sidewall spacers 55.

In some embodiments, the first gate sidewall spacers 55 are not incontact with the semiconductor wires 20. In certain embodiments, thesecond gate sidewall spacers 64 are not in contact with thesemiconductor wires 20.

FIGS. 3-21B show a sequential process for manufacturing a GAA FET deviceshown in FIGS. 1A-1D according to an embodiment of the presentdisclosure. It is understood that additional operations can be providedbefore, during, and after processes shown by FIGS. 3-21B, and some ofthe operations described below can be replaced or eliminated, foradditional embodiments of the method. The order of theoperations/processes may be interchangeable.

As shown in FIG. 3, impurity ions (dopants) 12 are implanted into asilicon substrate 10 to form a well region. The ion implantation isperformed to prevent a punch-through effect. In some embodiments, thesubstrate 10 includes a single crystalline semiconductor layer on atleast it surface portion. The substrate 10 may comprise a singlecrystalline semiconductor material such as, but not limited to Si, Ge,SiGe, GaAs, InSb, GaP, GaSb, InAlAs, InGaAs, GaSbP, GaAsSb and InP. Inone embodiment, the substrate 10 is made of crystalline Si.

The substrate 10 may include in its surface region, one or more bufferlayers (not shown). The buffer layers can serve to gradually change thelattice constant from that of the substrate to that of the source/drainregions. The buffer layers may be formed from epitaxially grown singlecrystalline semiconductor materials such as, but not limited to Si, Ge,GeSn, SiGe, GaAs, InSb, GaP, GaSb, InAlAs, InGaAs, GaSbP, GaAsSb, GaN,GaP, and InP. In a particular embodiment, the substrate 10 comprisessilicon germanium (SiGe) buffer layers epitaxially grown on the siliconsubstrate 10. The germanium concentration of the SiGe buffer layers mayincrease from 30 atomic % germanium for the bottom-most buffer layer to70 atomic % germanium for the top-most buffer layer. The substrate 10may include various regions that have been suitably doped withimpurities (e.g., p-type or n-type conductivity). The dopants 12 are,for example boron (BF₂) for an n-type Fin FET and phosphorus for ap-type Fin FET.

As shown in FIG. 4, stacked semiconductor layers are formed over thesubstrate 10. The stacked semiconductor layers include firstsemiconductor layers 20 and second semiconductor layers 25. Further, amask layer 15 is formed over the stacked layers.

The first semiconductor layers 20 and the second semiconductor layers 25are made of materials having different lattice constants, and mayinclude one or more layers of Si, Ge, SiGe, GaAs, InSb, GaP, GaSb,InAlAs, InGaAs, GaSbP, GaAsSb or InP.

In some embodiments, the first semiconductor layers 20 and the secondsemiconductor layers 25 are made of Si, a Si compound, SiGe, Ge or a Gecompound. In one embodiment, the first semiconductor layers 20 areSi_(1-x)Ge_(x), where x is more than about 0.5, or Ge (x=1.0) and thesecond semiconductor layers 25 are Si or Si_(1-y)Ge_(y), where y isequal to or less than about 0.6, and x>y. In this disclosure, an “M”compound” or an “M based compound” means the majority of the compound isM.

In FIG. 4, five layers of the first semiconductor layer 20 and fivelayers of the second semiconductor layer 25 are disposed. However, thenumber of the layers are not limited to five, and may be as small as 1(each layer) and in some embodiments, 2-20 layers of each of the firstand second semiconductor layers are formed. By adjusting the numbers ofthe stacked layers, a driving current of the GAA FET device can beadjusted.

The first semiconductor layers 20 and the second semiconductor layers 25are epitaxially formed over the substrate 10. The thickness of the firstsemiconductor layers 20 may be equal to or greater than that of thesecond semiconductor layers 25, and is in a range from about 5 nm toabout 50 nm in some embodiments, and is in a range from about 10 nm toabout 30 nm in other embodiments. The thickness of the secondsemiconductor layers 25 is in a range from about 5 nm to about 30 nm insome embodiments, and is in a range from about 10 nm to about 20 nm inother embodiments. The thickness of each of the first semiconductorlayers 20 may be the same, or may vary.

In some embodiments, the bottom first semiconductor layer (the closestlayer to the substrate 10) is thicker than the remaining firstsemiconductor layers. The thickness of the bottom first semiconductorlayer is in a range from about 10 nm to about 50 nm in some embodiments,or is in a range from 20 nm to 40 nm in other embodiments.

In some embodiments, the mask layer 15 includes a first mask layer 15Aand a second mask layer 15B. The first mask layer 15A is a pad oxidelayer made of a silicon oxide, which can be formed by a thermaloxidation. The second mask layer 15B is made of a silicon nitride (SiN),which is formed by chemical vapor deposition (CVD), including lowpressure CVD (LPCVD) and plasma enhanced CVD (PECVD), physical vapordeposition (PVD), atomic layer deposition (ALD), or other suitableprocess. The mask layer 15 is patterned into a mask pattern by usingpatterning operations including photo-lithography and etching.

Next, as shown in FIG. 5, the stacked layers of the first and secondsemiconductor layers 20, 25 are patterned by using the patterned masklayer, thereby the stacked layers are formed into fin structures 30extending in the X direction.

The fin structures 30 may be patterned by any suitable method. Forexample, the fin structures may be patterned using one or morephotolithography processes, including double-patterning ormulti-patterning processes. Generally, double-patterning ormulti-patterning processes combine photolithography and self-alignedprocesses, allowing patterns to be created that have, for example,pitches smaller than what is otherwise obtainable using a single, directphotolithography process. For example, in one embodiment, a sacrificiallayer is formed over a substrate and patterned using a photolithographyprocess. Spacers are formed alongside the patterned sacrificial layerusing a self-aligned process. The sacrificial layer is then removed, andthe remaining spacers, or mandrels, may then be used to pattern the finstructures.

In FIG. 5, two fin structures 30 are arranged in the Y direction. Butthe number of the fin structures is not limited to, and may be as smallas one and as large as three or more. In some embodiments, one or moredummy fin structures are formed on both sides of the fin structures 30to improve pattern fidelity in the patterning operations. As shown inFIG. 5, the fin structures 30 have upper portions constituted by thestacked semiconductor layers 20, 25 and well portions 11, whichcorresponds to the bottom fin structure.

The width W1 of the upper portion of the fin structure 30 along the Ydirection is in a range from about 10 nm to about 40 nm in someembodiments, and is in a range from about 20 nm to about 30 nm in otherembodiments. The height H1 along the Z direction of the fin structure 30is in a range from about 100 nm to about 200 nm.

After the fin structure is formed, an insulating material layer 41including one or more layers of insulating material is formed over thesubstrate so that the fin structures are fully embedded in theinsulating layer 41. The insulating material for the insulating layer 41may include silicon oxide, silicon nitride, silicon oxynitride (SiON),SiOCN, SiCN, fluorine-doped silicate glass (FSG), or a low-K dielectricmaterial, formed by LPCVD (low pressure chemical vapor deposition),plasma-CVD or flowable CVD. An anneal operation may be performed afterthe formation of the insulating layer 41. Then, a planarizationoperation, such as a chemical mechanical polishing (CMP) method and/oran etch-back method, is performed such that the upper surface of theuppermost second semiconductor layer 25 is exposed from the insulatingmaterial layer 41 as shown in FIG. 6.

In some embodiments, one or more fin liner layers 35 are formed over thestructure of FIG. 5 before forming the insulating material layer 41, asshown FIG. 6. The liner layer 35 is made of SiN or a siliconnitride-based material (e.g., SiON, SiCN or SiOCN). In some embodiments,the fin liner layers 35 include a first fin liner layer 35A formed overthe substrate 10 and side faces of the bottom fin structures 11, and asecond fin liner layer 35B formed on the first fin liner layer 35A. Eachof the liner layers has a thickness between about 1 nm and about 20 nmin some embodiments. In some embodiments, the first fin liner layer 35Aincludes silicon oxide and has a thickness between about 0.5 nm andabout 5 nm, and the second fin liner layer 35B includes silicon nitrideand has a thickness between about 0.5 nm and about 5 nm. The fin linerlayers 35 may be deposited through one or more processes such asphysical vapor deposition (PVD), chemical vapor deposition (CVD), oratomic layer deposition (ALD), although any acceptable process may beutilized.

Then, as shown in FIG. 7, the insulating material layer 41 is recessedto form an isolation insulating layer 40 so that the upper portions ofthe fin structures 30 are exposed. With this operation, the finstructures 30 are electrically separated from each other by theisolation insulating layer 40, which is also called a shallow trenchisolation (STI). In the embodiment shown in FIG. 7, the insulatingmaterial layer 41 is recessed until the bottommost first semiconductorlayer 20 is exposed. In other embodiments, the upper portion of the welllayer 11 is also partially exposed. The first semiconductor layers 20are sacrificial layers which are subsequently partially removed, and thesecond semiconductor layers 25 are subsequently formed into channellayers of a GAA FET.

After the isolation insulating layer 40 is formed, a sacrificial gatedielectric layer 52 is formed, as shown in FIG. 8. The sacrificial gatedielectric layer 52 includes one or more layers of insulating material,such as a silicon oxide-based material. In one embodiment, silicon oxideformed by CVD is used. The thickness of the sacrificial gate dielectriclayer 52 is in a range from about 1 nm to about 5 nm in someembodiments.

FIG. 9 illustrates a structure after a sacrificial gate structure 50 isformed over the exposed fin structures 30. The sacrificial gatestructure includes a sacrificial gate electrode 54 and the sacrificialgate dielectric layer 52. The sacrificial gate structure 50 is formedover a portion of the fin structure which is to be a channel region. Thesacrificial gate structure 50 defines the channel region of the GAA FET.

The sacrificial gate structure 50 is formed by first blanket depositingthe sacrificial gate dielectric layer 52 over the fin structures 30, asshown in FIG. 9. A sacrificial gate electrode layer is then blanketdeposited on the sacrificial gate dielectric layer and over the finstructures 30, such that the fin structures 30 are fully embedded in thesacrificial gate electrode layer. The sacrificial gate electrode layerincludes silicon such as polycrystalline silicon or amorphous silicon.The thickness of the sacrificial gate electrode layer is in a range fromabout 100 nm to about 200 nm in some embodiments. In some embodiments,the sacrificial gate electrode layer is subjected to a planarizationoperation. The sacrificial gate dielectric layer and the sacrificialgate electrode layer are deposited using CVD, including LPCVD and PECVD,PVD, ALD, or other suitable process. Subsequently, a mask layer isformed over the sacrificial gate electrode layer. The mask layerincludes a pad SiN layer 56 and a silicon oxide mask layer 58.

Next, a patterning operation is performed on the mask layer andsacrificial gate electrode layer is patterned into the sacrificial gatestructure 50, as shown in FIG. 9. The sacrificial gate structureincludes the sacrificial gate dielectric layer 52, the sacrificial gateelectrode layer 54 (e.g., poly silicon), the pad SiN layer 56 and thesilicon oxide mask layer 58. By patterning the sacrificial gatestructure, the stacked layers of the first and second semiconductorlayers are partially exposed on opposite sides of the sacrificial gatestructure, thereby defining source/drain (S/D) regions, as shown in FIG.9. In this disclosure, a source and a drain are interchangeably used andthe structures thereof are substantially the same. In FIG. 9, onesacrificial gate structure is formed, but the number of the sacrificialgate structures is not limited to one. Two or more sacrificial gatestructures are arranged in the X direction in some embodiments. Incertain embodiments, one or more dummy sacrificial gate structures areformed on both sides of the sacrificial gate structures to improvepattern fidelity.

After the sacrificial gate structure is formed, a blanket layer 53 of aninsulating material for gate sidewall spacers 55 is conformally formedby using CVD or other suitable methods, as shown in FIG. 10. The blanketlayer 53 is deposited in a conformal manner so that it is formed to havesubstantially equal thicknesses on vertical surfaces, such as thesidewalls, horizontal surfaces, and the top of the sacrificial gatestructure. In some embodiments, the blanket layer 53 is deposited to athickness in a range from about 2 nm to about 10 nm. In someembodiments, the insulating material of the blanket layer 53 is asilicon nitride-based material, such as SiN, SiON, SiOCN or SiCN andcombinations thereof. In certain embodiments, the insulating material isone of SiOC, SiCON and SiCN.

FIGS. 11A and 11B show the same structure as FIG. 10. FIG. 11A shows aperspective view and FIG. 11B shows a cross sectional view correspondingto line X1-X1 of FIG. 11A cutting the fin structure 30. In FIG. 11B thepad SiN layer 56 and the silicon oxide mask layer 58 are not shown.

Further, as shown in FIGS. 12A and 12B, the gate sidewall spacers 55 areformed on opposite sidewalls of the sacrificial gate structures byanisotropic etching, and subsequently, the S/D regions of the finstructure are recessed equal to or down below the upper surface of theisolation insulating layer 40. FIG. 12A shows a perspective view andFIG. 12B shows a cross sectional view corresponding to line X1-X1 ofFIG. 11A. In FIG. 12B the pad SiN layer 56 and the silicon oxide masklayer 58 are not shown.

After the blanket layer 53 is formed, anisotropic etching is performedon the blanket layer 53 using, for example, reactive ion etching (RIE).During the anisotropic etching process, most of the insulating materialis removed from horizontal surfaces, leaving the dielectric spacer layeron the vertical surfaces such as the sidewalls of the sacrificial gatestructures and the sidewalls of the exposed fin structures. The masklayer 58 may be exposed from the sidewall spacers. In some embodiments,an isotropic etching process may be subsequently performed to remove theinsulating material from the upper portions of the S/D region of theexposed fin structures 30.

Subsequently, the S/D regions of the fin structure are recessed downequal to or below the upper surface of the isolation insulating layer40, by using dry etching and/or wet etching. As shown in FIGS. 12A and12B, the sidewall spacers 55 formed on the S/D regions of the exposedfin structures are also removed. At this stage, end portions of thestacked layer of the first and second semiconductor layers 20, 25 underthe sacrificial gate structure have substantially flat faces which areflush with the sidewall spacers 55, as shown in FIG. 12B. In someembodiments, the end portions of the stacked layer of the first andsecond semiconductor layers 20, 25 are slightly horizontally etched.

Subsequently, as shown in FIGS. 13A and 13B, the second semiconductorlayers 25 are horizontally recessed (etched) so that edges of the secondsemiconductor layers 25 are located substantially below the gatesidewall spacers 55 and cavities 27 are formed. FIG. 13A shows aperspective view and FIG. 13B shows a cross sectional view correspondingto line X1-X1 of FIG. 11A cutting the fin structure 30. In FIG. 13B thepad SiN layer 56 and the silicon oxide mask layer 58 are not shown. Asshown in FIG. 13B, end portions (edges) of the second semiconductorlayers 25 have a concave shape such as a V-shape or a U-shape. The depthD1 of the recessing of the second semiconductor layers 25 from the planeincluding one gate sidewall spacer 55 is in a range from about 5 nm toabout 10 nm. The etching of the first semiconductor layer 25 includeswet etching and/or dry etching. A wet etchant such as atetramethylammonium hydroxide (TMAH) solution can be used to selectivelyetch the second semiconductor layers 25.

Then, as shown in FIGS. 14A and 14B, a dielectric material layer 60 isformed over the structure of FIGS. 13A and 13B. FIG. 14A shows aperspective view and FIG. 14B shows a cross sectional view correspondingto line X1-X1 of FIG. 11A cutting the fin structure 30. In FIG. 14B thepad SiN layer 56 and the silicon oxide mask layer 58 are not shown. Insome embodiments, the dielectric material layer 60 includes a siliconnitride-based material, such as SiN, SiON, SiOCN or SiCN andcombinations thereof and is different from the material of the gatesidewall spacers 55. In certain embodiments, the dielectric material issilicon nitride. The dielectric material layer 60 fully fills thecavities 27 as shown in FIG. 14B. The dielectric material layer 60 canbe formed using CVD, including LPCVD and PECVD, PVD, ALD, or othersuitable processes.

Next, as shown in FIGS. 15A and 15B, one or more etching operations areperformed to form dielectric inner spacers 62. FIG. 15A shows aperspective view and FIG. 15B shows a cross sectional view correspondingto line X1-X1 of FIG. 11A cutting the fin structure 30. In FIG. 15B thepad SiN layer 56 and the silicon oxide mask layer 58 are not shown. Theetching operations include one or more wet and/or dry etchingoperations. In certain embodiments, the etching is an isotropic etchingin some embodiments. The maximum thickness along the Y direction of thedielectric inner spacers 62 is in a range from about 0.5 nm to about 5nm in some embodiments. As shown in FIGS. 15A and 15B, a part of thedielectric material layer 60 remains over the bottom fin structure 11,while the dielectric material layer 60 formed on the gate sidewallspacers 55 and the isolation insulating layer 40 is removed.

Subsequently, as shown in FIGS. 16A and 16B, the first semiconductorlayers 20 are horizontally recessed (etched) so that edges of the firstsemiconductor layers 20 are located substantially below the gatesidewall spacers 55 and cavities 22 are formed. FIG. 16A shows aperspective view and FIG. 16B shows a cross sectional view correspondingto line X1-X1 of FIG. 11A. In FIG. 16B the pad SiN layer 56 and thesilicon oxide mask layer 58 are not shown. As shown in FIG. 16B, endportions (edges) of the first semiconductor layers 20 have a concaveshape such as a V-shape or a U-shape. The depth D2 of the recessing ofthe first semiconductor layers 20 from the plane including a surface ofone gate sidewall spacer 55 is in a range from about 7 nm to about 15nm. The etching of the first semiconductor layer 25 includes wet etchingand/or dry etching. A wet etchant such as an ammonium hydroxide (NH₄OH),tetramethylammonium solution can be used to selectively etch the firstsemiconductor layers 20. In some embodiments, D2 is greater than D1. Asshown in FIG. 16A, the first semiconductor layers 20 are separated fromthe gate sidewall spacers 55 and the dielectric inner spacers 62 by thisetching.

After the cavities 22 are formed, source/drain (S/D) epitaxial layers 80are formed, as shown in FIGS. 17A and 17B. FIG. 17A shows a perspectiveview and FIG. 17B shows a cross sectional view corresponding to lineX1-X1 of FIG. 11A. In FIG. 17B the pad SiN layer 56 and the siliconoxide mask layer 58 are not shown. The S/D epitaxial layer 80 includesone or more layers of Si, SiP, SiC and SiCP for an n-channel FET. TheS/D epitaxial layers 80 are formed by an epitaxial growth method usingCVD, ALD or molecular beam epitaxy (MBE). As shown in FIG. 17B, theinterface between at least one of the first semiconductor layers 20 andthe S/D epitaxial layer 80 is located under one of the gate sidewallspacers 55.

Subsequently, a liner layer 85 is formed and then an interlayerdielectric (ILD) layer 90 is formed, as shown in FIGS. 18A and 18B. FIG.18A shows a perspective view and FIG. 18B shows a cross sectional viewcorresponding to line X1-X1 of FIG. 11A.

The liner layer 85 is made of a silicon nitride-based material, such assilicon nitride, and functions as a contact etch stop layer (CESL) inthe subsequent etching operations. The materials for the ILD layer 90include compounds comprising Si, O, C and/or H, such as silicon oxide,SiCOH and SiOC. Organic materials, such as polymers, may be used for theILD layer 90. After the ILD layer 90 is formed, a planarizationoperation, such as CMP, is performed, so that the sacrificial gateelectrode layer 54 is exposed, as shown in FIGS. 18A and 18B.

Next, as shown in FIGS. 19A and 19B, the sacrificial gate electrodelayer 54 and sacrificial gate dielectric layer 52 are removed, therebyexposing a channel region of the fin structures in a space 59. FIG. 19Ashows a perspective view and FIG. 19B shows a cross sectional viewcorresponding to line X1-X1 of FIG. 11A. The ILD layer 90 protects theS/D epitaxial layers 80 during the removal of the sacrificial gatestructures. The sacrificial gate structures can be removed using plasmadry etching and/or wet etching. When the sacrificial gate electrodelayer 54 is polysilicon and the ILD layer 90 is silicon oxide, a wetetchant such as a TMAH solution can be used to selectively remove thesacrificial gate electrode layer 54. The sacrificial gate dielectriclayer 52 is thereafter removed using plasma dry etching and/or wetetching.

After the sacrificial gate structures are removed, the secondsemiconductor layers 25 in the channel region of the fin structures areremoved, thereby forming wires of the first semiconductor layers 20, asshown in FIGS. 20A and 20B. FIG. 20A shows a perspective view and FIG.20B shows a cross sectional view corresponding to line X1-X1 of FIG.11A.

The second semiconductor layers 25 can be removed or etched using anetchant that can selectively etch the second semiconductor layers 25.When the first semiconductor layers 20 are Si and the secondsemiconductor layers 25 are Ge or SiGe, the first semiconductor layers20 can be selectively removed using a wet etchant such as, but notlimited to, tetramethylammonium hydroxide (TMAH), ethylenediaminepyrocatechol (EDP), or potassium hydroxide (KOH) solution.

After the wires of the first semiconductor layers 20 are formed, a gatestructure 100 is formed, as shown in FIGS. 21A and 21B. FIG. 21A shows aperspective view and FIG. 21B shows a cross sectional view correspondingto line X1-X1 of FIG. 11A. A gate dielectric layer 104 is formed aroundeach channel layer (wires of the first semiconductor layers 20), and agate electrode layer 108 is formed over the gate dielectric layer 104.

In certain embodiments, the gate dielectric layer 104 includes one ormore layers of a dielectric material, such as silicon oxide, siliconnitride, or high-k dielectric material, other suitable dielectricmaterial, and/or combinations thereof. Examples of high-k dielectricmaterial include HfO₂, HfSiO, HfSiON, HfTaO, HfTiO, HfZrO, zirconiumoxide, aluminum oxide, titanium oxide, hafnium dioxide-alumina(HfO₂—Al₂O₃) alloy, other suitable high-k dielectric materials, and/orcombinations thereof. In some embodiments, an interfacial layer 102 isformed between the channel layers and the gate dielectric layer 104. Thegate dielectric layer 104 may be formed by CVD, ALD or any suitablemethod. In one embodiment, the gate dielectric layer 104 is formed usinga highly conformal deposition process such as ALD in order to ensure theformation of a gate dielectric layer having a uniform thickness aroundeach channel layer. The thickness of the gate dielectric layer 104 is ina range from about 1 nm to about 6 nm in one embodiment.

The gate electrode layer 108 is formed over the gate dielectric layer104 to surround each channel layer in some embodiments. The gateelectrode 108 includes one or more layers of conductive material, suchas polysilicon, aluminum, copper, titanium, tantalum, tungsten, cobalt,molybdenum, tantalum nitride, nickel silicide, cobalt silicide, TiN, WN,TiAl, TiAlN, TaCN, TaC, TaSiN, metal alloys, other suitable materials,and/or combinations thereof. The gate electrode layer 108 may be formedby CVD, ALD, electro-plating, or other suitable method. The gateelectrode layer is also deposited over the upper surface of the ILDlayer 90. The gate dielectric layer and the gate electrode layer formedover the ILD layer 90 are then planarized by using, for example, CMP,until the ILD layer 90 is revealed.

In certain embodiments, one or more work function adjustment layers 106are interposed between the gate dielectric layer 104 and the gateelectrode layer 108. The work function adjustment layers 106 are made ofa conductive material such as a single layer of TiN, TaN, TaAlC, TiC,TaC, Co, Al, TiAl, HfTi, TiSi, TaSi or TiAlC, or a multilayer of two ormore of these materials. For the n-channel FET, one or more of TaN,TaAlC, TiN, TiC, Co, TiAl, TiSi and TaSi is used as the work functionadjustment layer. The work function adjustment layer 106 may be formedby ALD, PVD, CVD, e-beam evaporation, or other suitable process.Further, the work function adjustment layer 106 may be formed separatelyfor the n-channel FET and the p-channel FET which may use differentmetal layers.

It is understood that the GAA FETs undergoes further CMOS processes toform various features such as contacts/vias, interconnect metal layers,dielectric layers, passivation layers, etc.

FIGS. 22A-31B show a sequential process for manufacturing a GAA FETdevice shown in FIGS. 2A-2D according to another embodiment of thepresent disclosure. It is understood that additional operations can beprovided before, during, and after processes shown by FIGS. 22A-31B, andsome of the operations described below can be replaced or eliminated,for additional embodiments of the method. The order of theoperations/processes may be interchangeable.

FIG. 22A shows a perspective view and FIG. 22B shows a cross sectionalview corresponding to line X1-X1 of FIG. 22A. In FIG. 22B the pad SiNlayer 56 and the silicon oxide mask layer 58 are not shown.

After the structure shown in FIGS. 11A and 11B is formed, anisotropicetching is performed on the blanket layer 53 using, for example,reactive ion etching (RIE). During the anisotropic etching process, mostof the insulating material is removed from horizontal surfaces, leavingthe dielectric spacer layer on the vertical surfaces such as the gatesidewalls 55 of the sacrificial gate structure 50. Further, theinsulating material 53 formed over the upper portions of the S/D regionof the exposed fin structures 30 is also removed, as shown in FIGS. 22Aand 22B. Thus, the stacked structure of the first semiconductor layers20 and the second semiconductor layer 25 is exposed at the S/D region.

Then, as shown in FIGS. 23A and 23B, the second semiconductor layers 25are horizontally recessed (etched) so that edges of the secondsemiconductor layers 25 are located substantially below the gatesidewall spacers 55 and cavities 27 are formed. FIG. 23A shows aperspective view and FIG. 23B shows a cross sectional view correspondingto line X1-X1 of FIG. 22A cutting the fin structure 30. In FIG. 23B thepad SiN layer 56 and the silicon oxide mask layer 58 are not shown. Asshown in FIG. 23B, end portions (edges) of the second semiconductorlayers 25 have a concave shape such as a V-shape or a U-shape in someembodiments. The depth D3 of the recessing of the second semiconductorlayers 25 from the plane including one gate sidewall spacer 55 is in arange from about 5 nm to about 10 nm. The etching of the firstsemiconductor layer 25 includes wet etching and/or dry etching. A wetetchant such as a tetramethylammonium hydroxide (TMAH) solution can beused to selectively etch the second semiconductor layers 25 against thefirst semiconductor layer 20.

Then, as shown in FIGS. 24A and 24B, a dielectric material layer 60 isformed over the structure of FIGS. 23A and 23B. FIG. 24A shows aperspective view and FIG. 24B shows a cross sectional view correspondingto line X1-X1 of FIG. 22A cutting the fin structure 30. In FIG. 24B thepad SiN layer 56 and the silicon oxide mask layer 58 are not shown. Insome embodiments, the dielectric material layer 60 includes a siliconnitride-based material, such as SiN, SiON, SiOCN or SiCN andcombinations thereof and is different from the material of the gatesidewall spacers 55. In certain embodiments, the dielectric material issilicon nitride. The dielectric material layer 60 fully fills thecavities 27 and the spaces between adjacent first semiconductor layers20, as shown in FIG. 24B. The dielectric material layer 60 can be formedusing CVD, including LPCVD and PECVD, PVD, ALD, or other suitableprocesses.

Next, as shown in FIGS. 25A and 25B, one or more etching operations areperformed to form dielectric inner spacers 62. FIG. 25A shows aperspective view and FIG. 25B shows a cross sectional view correspondingto line X1-X1 of FIG. 22A. In FIG. 25B the pad SiN layer 56 and thesilicon oxide mask layer 58 are not shown. The etching operationsinclude one or more wet and/or dry etching operations. In certainembodiments, the etching is an isotropic etching in some embodiments.The maximum thickness along the Y direction of the dielectric innerspacers 62 is in a range from about 0.5 nm to about 5 nm in someembodiments. As shown in FIGS. 25A and 25B, a part of the dielectricmaterial layer 60 remains over the bottom fin structure 11, and a partof the dielectric material 60 remains on the gate sidewall spacers 55 assecond gate sidewall spacers 64. In some embodiments, the thickness ofthe second gate sidewall spacers 64 is in a range from about 2 nm toabout 15 nm. The dielectric material layer 60 formed on the isolationinsulating layer 40 is removed.

Subsequently, as shown in FIGS. 26A and 26B, the first semiconductorlayers 20 are horizontally recessed (etched) so that edges of the firstsemiconductor layers 20 are located substantially below the gatesidewall spacers 55 and cavities 22 are formed. FIG. 26A shows aperspective view and FIG. 26B shows a cross sectional view correspondingto line X1-X1 of FIG. 22A. In FIG. 26B the pad SiN layer 56 and thesilicon oxide mask layer 58 are not shown. As shown in FIG. 26B, endportions (edges) of the first semiconductor layers 20 have a concaveshape such as a V-shape or a U-shape in some embodiments. The depth D4of the recessing of the first semiconductor layers 20 from the planeincluding a surface of one gate sidewall spacer 55 is in a range fromabout 7 nm to about 15 nm. The etching of the first semiconductor layer25 includes wet etching and/or dry etching. A wet etchant such as anammonium hydroxide (NH₄OH), tetramethylammonium solution can be used toselectively etch the first semiconductor layers 20 against the secondsemiconductor layer 25. In some embodiments, D4 is greater than D3. Asshown in FIG. 26A, the first semiconductor layers 20 are separated fromthe first gate sidewall spacers 55 and the second gate sidewall spacers64 by this etching.

After the cavities 22 are formed, source/drain (S/D) epitaxial layers 80are formed, as shown in FIGS. 27A and 27B. FIG. 27A shows a perspectiveview and FIG. 27B shows a cross sectional view corresponding to lineX1-X1 of FIG. 22A. In FIG. 27B the pad SiN layer 56 and the siliconoxide mask layer 58 are not shown. The S/D epitaxial layer 80 includesone or more layers of Si, SiP, SiC and SiCP for an n-channel FET. TheS/D epitaxial layers 80 are formed by an epitaxial growth method usingCVD, ALD or molecular beam epitaxy (MBE). As shown in FIG. 27B, theinterface between at least one of the first semiconductor layers 20 andthe S/D epitaxial layer 80 is located under one of the gate sidewallspacers 55.

Subsequently, a liner layer 85 is formed and then an interlayerdielectric (ILD) layer 90 is formed, as shown in FIGS. 28A and 28B. FIG.28A shows a perspective view and FIG. 28B shows a cross sectional viewcorresponding to line X1-X1 of FIG. 22A.

The liner layer 85 is made of a silicon nitride-based material, such assilicon nitride, and functions as a contact etch stop layer (CESL) inthe subsequent etching operations. The materials for the ILD layer 90include compounds comprising Si, O, C and/or H, such as silicon oxide,SiCOH and SiOC. Organic materials, such as polymers, may be used for theILD layer 90. After the ILD layer 90 is formed, a planarizationoperation, such as CMP, is performed, so that the sacrificial gateelectrode layer 54 is exposed, as shown in FIGS. 28A and 28B.

Next, as shown in FIGS. 29A and 29B, the sacrificial gate electrodelayer 54 and sacrificial gate dielectric layer 52 are removed, therebyexposing a channel region of the fin structures. FIG. 29A shows aperspective view and FIG. 29B shows a cross sectional view correspondingto line X1-X1 of FIG. 22A. The ILD layer 90 protects the S/D epitaxiallayers 80 during the removal of the sacrificial gate structures. Thesacrificial gate structures can be removed using plasma dry etchingand/or wet etching. When the sacrificial gate electrode layer 54 ispolysilicon and the ILD layer 90 is silicon oxide, a wet etchant such asa TMAH solution can be used to selectively remove the sacrificial gateelectrode layer 54. The sacrificial gate dielectric layer 52 isthereafter removed using plasma dry etching and/or wet etching.

After the sacrificial gate structures are removed, the secondsemiconductor layers 25 in the channel region of the fin structures areremoved, thereby forming wires of the first semiconductor layers 20, asshown in FIGS. 30A and 30B. FIG. 30A shows a perspective view and FIG.20B shows a cross sectional view corresponding to line X1-X1 of FIG.22A.

The second semiconductor layers 25 can be removed or etched using anetchant that can selectively etch the second semiconductor layers 25.When the first semiconductor layers 20 are Si and the secondsemiconductor layers 25 are Ge or SiGe, the first semiconductor layers20 can be selectively removed using a wet etchant such as, but notlimited to, tetramethylammonium hydroxide (TMAH), ethylenediaminepyrocatechol (EDP), or potassium hydroxide (KOH) solution.

After the wires of the first semiconductor layers 20 are formed, a gatestructure 100 is formed, as shown in FIGS. 31A and 31B. FIG. 31A shows aperspective view and FIG. 21B shows a cross sectional view correspondingto line X1-X1 of FIG. 31A. A gate dielectric layer 104 is formed aroundeach channel layer (wires of the first semiconductor layers 20), and agate electrode layer 108 is formed over the gate dielectric layer 104.

In certain embodiments, the gate dielectric layer 104 includes one ormore layers of a dielectric material, such as silicon oxide, siliconnitride, or high-k dielectric material, other suitable dielectricmaterial, and/or combinations thereof. Examples of high-k dielectricmaterial include HfO₂, HfSiO, HfSiON, HfTaO, HfTiO, HfZrO, zirconiumoxide, aluminum oxide, titanium oxide, hafnium dioxide-alumina(HfO₂—Al₂O₃) alloy, other suitable high-k dielectric materials, and/orcombinations thereof. In some embodiments, an interfacial layer 102 isformed between the channel layers and the gate dielectric layer 104. Thegate dielectric layer 104 may be formed by CVD, ALD or any suitablemethod. In one embodiment, the gate dielectric layer 104 is formed usinga highly conformal deposition process such as ALD in order to ensure theformation of a gate dielectric layer having a uniform thickness aroundeach channel layer. The thickness of the gate dielectric layer 104 is ina range from about 1 nm to about 6 nm in one embodiment.

The gate electrode layer 108 is formed over the gate dielectric layer104 to surround each channel layer in some embodiments. The gateelectrode 108 includes one or more layers of conductive material, suchas polysilicon, aluminum, copper, titanium, tantalum, tungsten, cobalt,molybdenum, tantalum nitride, nickel silicide, cobalt silicide, TiN, WN,TiAl, TiAlN, TaCN, TaC, TaSiN, metal alloys, other suitable materials,and/or combinations thereof. The gate electrode layer 108 may be formedby CVD, ALD, electro-plating, or other suitable method. The gateelectrode layer is also deposited over the upper surface of the ILDlayer 90. The gate dielectric layer and the gate electrode layer formedover the ILD layer 90 are then planarized by using, for example, CMP,until the ILD layer 90 is revealed.

In certain embodiments, one or more work function adjustment layers 106are interposed between the gate dielectric layer 104 and the gateelectrode layer 108. The work function adjustment layers 106 are made ofa conductive material such as a single layer of TiN, TaN, TaAlC, TiC,TaC, Co, Al, TiAl, HfTi, TiSi, TaSi or TiAlC, or a multilayer of two ormore of these materials. For the n-channel FET, one or more of TaN,TaAlC, TiN, TiC, Co, TiAl, HfTi, TiSi and TaSi is used as the workfunction adjustment layer. The work function adjustment layer 106 may beformed by ALD, PVD, CVD, e-beam evaporation, or other suitable process.Further, the work function adjustment layer 106 may be formed separatelyfor the n-channel FET and the p-channel FET which may use differentmetal layers.

It is understood that the GAA FETs undergoes further CMOS processes toform various features such as contacts/vias, interconnect metal layers,dielectric layers, passivation layers, etc.

The various embodiments or examples described herein offer severaladvantages over the existing art. For example, in the presentdisclosure, the channels (semiconductor wires) are not in contact withgate sidewall spacers and the gate sidewall spacers are in contact withthe source/drain epitaxial layer (SiP layer). Thus, it is possible toreduce interfacial state density (Dit) under the gate sidewall spacers.Further, by using a larger band gap material than the Ge or SiGe of thechannels to contact the ends of the channels, it is possible to reduceGe band-to-band channel leakage. In addition, since a remaining layer ofthe dielectric material layer is disposed at the bottom of thesource/drain epitaxial layer, it is possible to reduce substrate leakagecurrent.

It will be understood that not all advantages have been necessarilydiscussed herein, no particular advantage is required for allembodiments or examples, and other embodiments or examples may offerdifferent advantages.

In accordance with one aspect of the present disclosure, in a method ofmanufacturing a semiconductor device, a fin structure, in which firstsemiconductor layers and second semiconductor layers are alternatelystacked, is formed over a bottom fin structure. A sacrificial gatestructure having sidewall spacers is formed over the fin structure. Thesidewall spacers is formed in a direction perpendicular to a majorsurface of a semiconductor substrate. A source/drain region of the finstructure, which is not covered by the sacrificial gate structure, isremoved. The second semiconductor layers are laterally recessed.Dielectric inner spacers are formed on lateral ends of the recessedsecond semiconductor layers. The first semiconductor layers arelaterally recessed. A source/drain epitaxial layer is formed to contactlateral ends of the recessed first semiconductor layer. The secondsemiconductor layers are removed thereby releasing the firstsemiconductor layers in a channel region. A gate structure is formedaround the first semiconductor layers. In one or more of the foregoingand the following embodiments, an interface between at least one of thefirst semiconductor layers and the source/drain epitaxial layer islocated under one of the sidewall spacers. In one or more of theforegoing and the following embodiments, the interface is located closerto the gate structure than a center line of the one of the sidewallspacers. In one or more of the foregoing and the following embodiments,the sidewall spacers are not in contact with the first semiconductorlayers. In one or more of the foregoing and the following embodiments,the forming dielectric inner spacers includes forming a dielectric layerand etching the dielectric layer, and the source/drain epitaxial layeris separated from the bottom fin structure by a part of the dielectriclayer. In one or more of the foregoing and the following embodiments, amaterial of the sidewall spacers is different from a material of thedielectric inner spacers. In one or more of the foregoing and thefollowing embodiments, the material of the dielectric inner spacers issilicon nitride. In one or more of the foregoing and the followingembodiments, the material of the sidewall spacers is one of SiOC, SiCONand SiCN. In one or more of the foregoing and the following embodiments,the first semiconductor layers are made of Ge or Si_(1-x)Ge_(x), where0.5≤x<1, and the second semiconductor layers are made of Si_(1-y)Ge_(y),where 0.2≤y≤0.6, and x>y.

In accordance with another aspect of the present disclosure, in a methodof manufacturing a semiconductor device, a fin structure, in which firstsemiconductor layers and second semiconductor layers are alternatelystacked, is formed over a bottom fin structure. A sacrificial gatestructure having sidewall spacers is formed over the fin structure. Thesidewall spacers is formed in a direction perpendicular to a majorsurface of a semiconductor substrate. The second semiconductor layers ina source/drain region of the fin structure, which is not covered by thesacrificial gate structure, are removed. A dielectric layer is formed.The dielectric layer and the first semiconductor layers in thesource/drain region are etched, thereby forming dielectric inner spacerson lateral ends of the second semiconductor layers. The firstsemiconductor layers are laterally recessed. A source/drain epitaxiallayer is formed to contact lateral ends of the recessed firstsemiconductor layer. The second semiconductor layers are removed therebyreleasing the first semiconductor layers in a channel region. A gatestructure is formed around the first semiconductor layers. In one ormore of the foregoing and the following embodiments, an interfacebetween at least one of the first semiconductor layers and thesource/drain epitaxial layer is located under one of the sidewallspacers. In one or more of the foregoing and the following embodiments,the sidewall spacers are not in contact with the first semiconductorlayers. In one or more of the foregoing and the following embodiments, amaterial of the sidewall spacers is different from a material of thedielectric inner spacers. In one or more of the foregoing and thefollowing embodiments, the material of the dielectric inner spacers issilicon nitride. In one or more of the foregoing and the followingembodiments, the material of the sidewall spacers is one of SiOC, SiCONand SiCN. In one or more of the foregoing and the following embodiments,the first semiconductor layers are made of Ge or Si_(1-x)Ge_(x), where0.5≤x<1 and the second semiconductor layers are made of Si_(1-y)Ge_(y),where 0.2≤y≤0.6, and x>y. In one or more of the foregoing and thefollowing embodiments, a part of the dielectric layer remains on thesidewall spacers after the dielectric inner spacers are formed. In oneor more of the foregoing and the following embodiments, the source/drainepitaxial layer is separated from the bottom fin structure by a part ofthe dielectric layer.

In accordance with another aspect of the present disclosure, in a methodof manufacturing a semiconductor device, a fin structure, in which firstsemiconductor layers and second semiconductor layers are alternatelystacked, is formed over a bottom fin structure. A sacrificial gatestructure is formed over the fin structure. Sidewall spacers are formedon opposing side faces of the sacrificial gate structure. A source/drainregion of the fin structure is removed. The second semiconductor layersare laterally recessed. Dielectric inner spacers are formed on lateralends of the recessed second semiconductor layers. The firstsemiconductor layers are laterally recessed. A source/drain epitaxiallayer is formed to contact lateral ends of the recessed firstsemiconductor layer. An interlayer dielectric layer is formed. Thesacrificial gate structure is removed. The second semiconductor layersare removed, thereby releasing the first semiconductor layers in achannel region. A gate structure around the first semiconductor layers.In one or more of the foregoing and the following embodiments, amaterial of the sidewall spacers is different from a material of thedielectric inner spacers.

In accordance with one aspect of the present disclosure, a semiconductordevice includes semiconductor wires vertically arranged, each of whichhas a channel region, a source/drain epitaxial layer connected to endsof the semiconductor wires, a gate structure having sidewall spacersformed around the semiconductor wires, and dielectric inner spacersdisposed between the gate structure and the source/drain epitaxiallayer. An interface between at least one of the semiconductor wires andthe source/drain epitaxial layer is located under one of the sidewallspacers. In one or more of the foregoing and the following embodiments,the sidewall spacers are not in contact with the semiconductor wires. Inone or more of the foregoing and the following embodiments, theinterface is located closer to the gate structure than a center line ofthe one of the sidewall spacers. In one or more of the foregoing and thefollowing embodiments, the ends of the semiconductor wires have aV-shape or U-shape cross section. In one or more of the foregoing andthe following embodiments, a material of the sidewall spacers isdifferent from a material of the dielectric inner spacers. In one ormore of the foregoing and the following embodiments, the material of thedielectric inner spacers is silicon nitride. In one or more of theforegoing and the following embodiments, the material of the sidewallspacers is one of SiOC, SiCON and SiCN. In one or more of the foregoingand the following embodiments, the semiconductor wires are made of Ge orSi_(1-x)Ge_(x), where 0.5≤x<1.0. In one or more of the foregoing and thefollowing embodiments, the source/drain epitaxial lays includes SiP. Inone or more of the foregoing and the following embodiments, an entiretyof the dielectric inner spacers is located under the sidewall spacers.

In accordance with another aspect of the present disclosure, asemiconductor device includes semiconductor wires vertically arranged,each of which has a channel region, a source/drain epitaxial layerconnected to ends of the semiconductor wires, a gate structure havingfirst sidewall spacers formed around the semiconductor wires, dielectricinner spacers disposed between the gate structure and the source/drainepitaxial layer, and second sidewall spacers disposed on the firstsidewall spacers. The first sidewall spacers are not in contact with thesemiconductor wires. In one or more of the foregoing and the followingembodiments, the second sidewall spacers are not in contact with thesemiconductor wires. In one or more of the foregoing and the followingembodiments, an interface between at least one of the semiconductorwires and the source/drain epitaxial layer is located under one of thefirst sidewall spacers. In one or more of the foregoing and thefollowing embodiments, an interface between at least one of thedielectric inner spacers and the source/drain epitaxial layers islocated outside a region under one of the first sidewall spacers. In oneor more of the foregoing and the following embodiments, a material ofthe second sidewall spacers and a material of the dielectric innerspacers are the same. In one or more of the foregoing and the followingembodiments, a material of the first sidewall spacers is different fromthe material of the dielectric inner spacers. In one or more of theforegoing and the following embodiments, the material of the dielectricinner spacers is silicon nitride. In one or more of the foregoing andthe following embodiments, the material of the first sidewall spacers isone of SiOC, SiCON and SiCN. In one or more of the foregoing and thefollowing embodiments, the semiconductor wires are made of Ge orSi_(1-x)Ge_(x), where 0.5≤x<1.0.

In accordance with another aspect of the present disclosure, asemiconductor device includes semiconductor wires vertically arranged,each of which has a channel region, a source/drain epitaxial layerconnected to ends of the semiconductor wires, a gate structure havingsidewall spacers formed around the semiconductor wires, and dielectricinner spacers disposed between the gate structure and the source/drainepitaxial layer. The sidewall spacers are not in contact with thesemiconductor wires.

The foregoing outlines features of several embodiments or examples sothat those skilled in the art may better understand the aspects of thepresent disclosure. Those skilled in the art should appreciate that theymay readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodiments orexamples introduced herein. Those skilled in the art should also realizethat such equivalent constructions do not depart from the spirit andscope of the present disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. A method of manufacturing a semiconductor device,comprising: forming a fin structure in which first semiconductor layersand second semiconductor layers are alternately stacked over a bottomfin structure; forming a sacrificial gate structure having sidewallspacers over the fin structure, the sidewall spacers being formed in adirection perpendicular to a major surface of a semiconductor substrate;removing a source/drain region of the fin structure, which is notcovered by the sacrificial gate structure; laterally recessing thesecond semiconductor layers; forming dielectric inner spacers on lateralends of the recessed second semiconductor layers; laterally recessingthe first semiconductor layers; forming a source/drain epitaxial layerto contact lateral ends of the recessed first semiconductor layers;removing the second semiconductor layers thereby releasing the firstsemiconductor layers in a channel region; and forming a gate structurearound the first semiconductor layers, wherein end portions of the firstand second semiconductor layers have a concave shape.
 2. The method ofclaim 1, wherein an interface between at least one of the firstsemiconductor layers and the source/drain epitaxial layer is locatedunder one of the sidewall spacers.
 3. The method of claim 2, wherein theinterface is located closer to the gate structure than a center line ofthe one of the sidewall spacers.
 4. The method of claim 1, wherein thesidewall spacers are not in contact with the first semiconductor layers.5. The method of claim 1, wherein: the forming dielectric inner spacersincludes forming a dielectric layer and etching the dielectric layer,and the source/drain epitaxial layer is separated from the bottom finstructure by a part of the dielectric layer.
 6. The method of claim 1,wherein a material of the sidewall spacers is different from a materialof the dielectric inner spacers.
 7. The method of claim 6, wherein thematerial of the dielectric inner spacers is silicon nitride.
 8. Themethod of claim 6, wherein the material of the sidewall spacers is oneof SiOC, SiCON and SiCN.
 9. The method of claim 1, wherein the firstsemiconductor layers are made of Ge or Si_(1-x)Ge_(x), where 0.5≤x<1,and the second semiconductor layers are made of Si_(1-y)Ge_(y), where0.2≤y≤0.6, and x>y.
 10. A method of manufacturing a semiconductordevice, comprising: forming a fin structure in which first semiconductorlayers and second semiconductor layers are alternately stacked over abottom fin structure; forming a sacrificial gate structure havingsidewall spacers over the fin structure, the sidewall spacers beingformed in a direction perpendicular to a major surface of asemiconductor substrate; removing the second semiconductor layers in asource/drain region of the fin structure, which is not covered by thesacrificial gate structure; forming a dielectric layer; etching thedielectric layer and the first semiconductor layers in the source/drainregion, thereby forming dielectric inner spacers on lateral ends of thesecond semiconductor layers; laterally recessing the first semiconductorlayers; forming a source/drain epitaxial layer to contact lateral endsof the recessed first semiconductor layers; removing the secondsemiconductor layers thereby releasing the first semiconductor layers ina channel region; and forming a gate structure around the firstsemiconductor layers, wherein a part of the dielectric layer remains onthe sidewall spacers after the dielectric inner spacers are formed. 11.The method of claim 10, wherein an interface between at least one of thefirst semiconductor layers and the source/drain epitaxial layer islocated under one of the sidewall spacers.
 12. The method of claim 10,wherein the sidewall spacers are not in contact with the firstsemiconductor layers.
 13. The method of claim 10, wherein a material ofthe sidewall spacers is different from a material of the dielectricinner spacers.
 14. The method of claim 13, wherein the material of thedielectric inner spacers is silicon nitride.
 15. The method of claim 13,wherein the material of the sidewall spacers is one of SiOC, SiCON andSiCN.
 16. The method of claim 10, wherein the first semiconductor layersare made of Ge or Si_(1-x)Ge_(x), where 0.5≤x<1, and the secondsemiconductor layers are made of Si_(1-y)Ge_(y), where 0.2≤y≤0.6, andx>y.
 17. The method of claim 10, wherein another part of the dielectriclayer remains on the bottom fin structure and is in contact with thesource/drain epitaxial layer.
 18. The method of claim 10, wherein thesource/drain epitaxial layer is separated from the bottom fin structureby a part of the dielectric layer.
 19. A semiconductor device,comprising: semiconductor wires vertically arranged, each of which has achannel region; a source/drain epitaxial layer connected to ends of thesemiconductor wires; a gate structure having sidewall spacers formedaround the semiconductor wires; and dielectric inner spacers disposedbetween the gate structure and the source/drain epitaxial layer, whereinan interface between at least one of the semiconductor wires and thesource/drain epitaxial layer is located closer to the gate structurethan an interface between at least one of the dielectric inner spacersand the source/drain epitaxial layer, and the interface between the atleast one of the dielectric inner spacers and the source/drain epitaxiallayer is located closer to an outer side face of one of the sidewallspacers than an inner side face of one of the sidewall spacers.
 20. Thesemiconductor device of claim 19, wherein the sidewall spacers are notin contact with the semiconductor wires.